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What I'd like to do first is address the aspect of varying fuel pressure at idle. What follows is a guide that we have begun to add to turbosystems. We have also provided this info to those in the field who had questions. ======================================
Understanding and Working With the Billet Fuel Injection Control Unit
Your Hahn RaceCraft Fuel Injection Control Unit (FICU) is a precision fuel regulation device designed to provide correct engine fueling to accommodate your turbosystem over a variety of conditions. Your engine?s fuel needs vary over a wide range, more so once you add turbocharging. The FICU, when set up correctly, will react to your engine?s changes in load and manifold pressure. The FICU's reactions to engine changes maintain an optimal air-fuel ratio at all times.
The FICU uses manifold pressure as a reference in determining the correct fuel delivery. When describing manifold pressure, both intake vacuum and boost pressure are included. Intake vacuum is typically expressed in inches of mercury (or in/hg.), while boost pressure is expressed in PSI. The critical aspect in understanding and working well with the FICU is to realize that it uses these changes in manifold vacuum/pressure to determine the correct fuel flow. Just as differences in boost pressure will affect the fuel delivery, so will changes in intake vacuum, such as at idle.
Idle manifold vacuum is not always the same value. It is not unusual to see a range of 5in/hg in vacuum change on a normal engine. What will cause such a large range? Primarily, engine temperature and load. Vacuum on a cold engine is different (typically higher) than on a warm engine. Load changes also affect vacuum, especially on four cylinder engines. Such loads include air conditioning, power steering, cooling fans, heavy alternator loads due to discharged batteries or huge stereos, etc.
Of course, as the engine vacuum changes, so does the FICU?s reaction. When idle vacuum is stronger, fuel pressure will be less, and when vacuum decreases, fuel pressure will rise. What can seem surprising is the amount of change: during normal variation in engine vacuum for any of the reasons noted above, fuel pressure will also vary, sometimes as much as ten to 15 PSI. Why so much change for what seems like a small change in vacuum? Bear in mind, the FICU is a variable device that allows for large fuel pressure changes, not only under boost, but during vacuum too: a change in vacuum of only 5 inches will result in a fuel pressure change of 15 PSI!
Your FICU?s behavior during vacuum changes is very intentional, and quite effective. It allows your turbocharged engine to achieve an optimal air-fuel ratio at all times, not just during boost. These air-fuel changes during part throttle vacuum conditions are critical to smooth drivability behavior.
How, then, should one interpret and adjust fuel pressure? Ideally, only adjust idle fuel pressure with the engine fully warmed up, and all accessories as well as cooling fan off. Adjust to the range specified in your Turbosystem Installation manual. For future reference, also record the vacuum reading (you will see it on your vacuum/boost gauge). Should you suspect a need to readjust in the future, simply repeat the conditions, while ensuring that the engine is operating at the same vacuum reading as when you last checked. If the pressure is within three PSI of the last time you set it, all is well.
Of course, if you monitor fuel pressure all the time with an in-car gauge, you will see the entire range of different idle fuel pressures your FICU achieves. If you are doing this, also view the vacuum gauge. You will soon learn the correlation between these two variables of boost and vacuum: even though they vary, they have a direct relationship with one another: when vacuum is higher, fuel pressure will be lower, and always in the same amount.
One last thing: does the variation in idle fuel pressure affect maximum fuel pressure achieved under boost? No, as vacuum induced changes in fuel pressure do not affect the FICU?s behavior under boost. The only time you need to re-check your boosted fuel pressure is if you adjust the center screw in the FICU.
Hahn RaceCraft continues to refine fuel system design as it applies to turbocharging, and the FICU is no exception. We will soon introduce more FICU models and options for FICU equipped vehicles. Please contact us if you have any questions or needs, and we will update you on the latest developments!
=========================== That's our official line, as sent out to the public; what follows now are some comments and insights I'd like to add:
There are many points to consider in reference to this comparison of other product to the regulator we use. Some of these points make a truly direct comparison difficult to achieve. Therefore, I ask that those who would take exception with any of these points below please consider the whole picture before engaging me in detailed debate about any one aspect.
1. The Vortech SFMU component is designed to be the ultimate of all rising rate regulators, and I commend it for that. It is also the most expensive! Yet, many aspects of our cars are also not the ultimate of what's available: many choices are based upon what we can afford. If we could all afford the best of everything, we would not be driving 2GNT's! Certainly, HRC could use this product, and the price of the system would rise accordingly: I do not think that this complex and expensive of a product is required to perform the task at hand.
2. The Vortech unit may respond to vacuum differently than our unit. I cannot say for sure, but I can assure you of this: if it uses the same rate of gain for vacuum that it does for boost (like ours), then it would have to also vary fuel pressure based upon changes in manifold vacuum. If it is hooked up the same way, and never, ever changes at idle as stated here, then it is most certainly not referencing manifold vacuum in the same fashion as ours.
3. We have intentionally referenced the fuel pressure to change at a large rate with vacuum. The intent is to cure an otherwise lean condition that will occur at low vacuum / almost boost conditions. In testing, when we set up the regulator to run a fixed pressure until boost is achieved, a lean condition was noted in this region. Sure, idle pressure was rock solid, but the lean part throttle aspect was unacceptable. The thing to keep in mind: your engine is actually being 'supercharged' (more air than without a turbo) well before actual gauge 'boost' occurs. She needs more fuel to accomodate this additional air, and our approach provides it.
4. Comparisons to 1:1 regs (like Jason notes with the Aeromotive) are not germaine to this conversation: of course they will be more steady, with only a fraction of the rate of change vs. vacuum that our FICU is intended to achieve.
5. Interestingly, the only time we hear about this fluctuation is on cars equipped to allow the driver to view fuel pressure all the time. Systems that are installed with the gauge used temporarily for setup and then removed never result in reports of fluctuations. Well, no kidding, right? But what this means to us is that those systems where the pressure is not being scrutinized are also not exhibiting driveability problems, and that therefore, there are no variations excessive enough to cause a problem. Only when the pressure is being looked at through the entire varying range seen during daily operation do we hear of a 'problem', and even then, the cars still run quite well, it's just gauge activity that is questioned.
6. The total number of actual inquiries on this aspect is but a fraction of the total kits sold. This is not to minimize the concerns of those who discuss this issue here, but to demonstrate that, contrary to the idea one might get from viewing posts here, the question is not at all widespread. No offense, folks, but Internet boards tend to whip up more of a lather over these types of issues, as folks feed off each other's opinions and 'expert' advice. One must also look at things from the Big Perspective to gain a truly accurate sample.
7. The closed-loop fuel system on these cars is marvelous at correcting for slight pressure variations. I recommend that one base whether or not they have a pressure variation problem on how the car runs, as opposed to what the gauge does. As far as what the gauge does, keep in mind the natural variations that will occur as a result of the points outlined above. If it ain't broke, don't fix it!
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Fuel Mappers
Jason, love ya, but you have left out one very important telephone conversation you and I had on this subject. I had hoped you would mention it by now, but as it does not support your 'position', you may have unintentionally left it out:
Any time one adds as much as a voltmeter to the MAP sensor circuit, the total circuit impedance is changed, and the interaction of the devices (MAP sensor, Fuel Mapper, ECU) can be affected. The addition of a Super AFC is a huge change, partially because its designed function is to change MAP voltage. Simply adding it to the circuit changes the impedance, even with all 'zeros' in the tables. Thus, the voltage seen on its readout will be different. Like those who view fuel pressure all the time, the only instances we have seen so far of a 'voltage issue' on the MAP circuit are from those with AFC's.
Now, before you folks with Scanners or Voltmeters cry foul, allow me to lay this on you: many factors beyond our control can also affect the ultimate MAP sensor voltage. These include sensor and harness issues, poor connections, corroded terminals, etc. What we do with every single Mapper is to bench calibrate them using a 5 volt reference, a new (known good) MAP sensor, and pressurized air. Every one is tested and set to within .05 volt, or 1%. We can't do better than that!
So, you might say, if there are possible variations on the car itself, why not allow the installer to calibrate it himself once installed? We've decided against it as too dangerous for the mainstream, as a misadjustment can be a BIG problem, and correctly hooking up a DVOM and then watching it during full boost operation...well, you can see what I mean. It's better this way.
FWIW, the MAP voltage range from about 3.9 to 4.5 volts is all interpreted by the ECU as full load: there is little difference in pulse width, and thus the fuel delivered to the engine is almost identical throughout that range.
Now, are there enough variations on cars themselves to warrant a different approach? No, based upon our testing and customer feedback. I had personally asked Jason to revisit his opinions after calling his attention to some of the above mentioned aspects, but I have not heard back from him. That's cool, I know that we are all very busy. But let's all talk on the same page: HRC is very dependent upon good backput from inquisitive, intelligent (but still amateur, after all) folks like Jason. Without it, we cannot identify and alleviate issues that occur in the field. All I ask is, don't be two-faced: if it's important enough to discuss in detail here, sharing info with us is equally important, especially if not sharing it with us can potentially lead to our products being cast in an unfavorable light, or prevent us from making corrections to benefit all.
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Manifold Bolts
Yes, they are a pain! I'm sorry about that, but invest in a quality ball-end 6mm driver for best results. The shape of our manifold has dictated that we use these pesky Allen bolts. We feel it is a worthy compromise to support a manifold that is very durable and the most powerful available (9.80's @ 151 MPH, who else can say THAT?).
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As a 'closer', I'd like to add that the best place for straight talk about our systems is our Tech Support Department. No one knows these cars or turbosystems better than us, and we are always willing to help. Call 630-801-9065 any weekday afternoon and speak directly to "Smilin" Len Ayala. The driver and co-owner of the world's Baddest 2.0 420A is always there for you. You can also email Tech: tech@turbosystem.com.
Thanks for your time, sorry for the long post, Bill Hahn Jr.
Bill Hahn Jr. 98 RS Turbo: 10.87 @ 136 MPH HRC Stage V with N20 Nation's Fastest Street FWD 2G DSM www.turbosystem.com
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